Apparatus for indicating the thermal history of deep-freeze products particularly foods

ABSTRACT

A system for indicating the conditions of storage and treatment of deep-frozen goods which consists of a sealed receptacle containing a pair of interactable components, one of which is flowable while the other is absorptive and capable of producing a visible indication of the degree of interaction. The liquid component is retained in a closed vessel within the receptacle and, also within the receptacle, means is provided for permitting escape of the liquid at a predetermined instant. The liquid is separated from its coacting component also by a liquid-soluble barrier which may be omitted in limited regions to permit direct action immediately upon openings of the liquid-storage vessel and thereby indicate directly the fact that the device is functioning.

United States Patent Johann Michel Ulmerstrasse 160a;

Charlotte Keller, Blutenstrasse 4; Hans- Joachim Keller, Blutenstrasse4, allot [72] Inventors Augsburg, Germany [21] Appl. No. 690,456 [22]Filed Dec. 14, 1967 [45] Patented Oct. 26, 1971 [32] Priority Dec. 19,1966 [33] Germany [31] M 72071 [54] APPARATUS FOR INDICATING THE THERMALHISTORY OF DEEP-FREEZE PRODUCTS 7 Primary Examiner-Norman YudkoffAssistant Examiner-F. E. Drummond AttameyKarl F. Ross ABSTRACT: A systemfor indicating the conditions of storage and treatment of deep-frozengoods which consists of a sealed receptacle containing a pair ofinteractable components, one of which is flowable while the other isabsorptive and capable of producing a visible indication of the degreeof interaction. The liquid component is retained in a closed vesselwithin the receptacle and, also within the receptacle, means is providedfor permitting escape of the liquid at a predetermined instant. Theliquid is separated from its coacting component also by a liquid-solublebarrier which may be omitted in limited regions to permit direct actionimmediately upon openings of the liquid-storage vessel and therebyindicate directly the fact that the device is functioning.

PATENTEUOET 26 I97! SHEET 1 [1F 4 J nhann MICHEL Charlotte KELLERHans-Joachim KE LER INVENTO Toss Attorney PATENTEDUCT 2s I97l 3,615,719

sum 2 BF 4 Johann MICHEL Charlotte KELLER Hans-J oachim KELIE RINVENTORS Aiioiiu-gy PATENTEUum 26 I97! 3,615,719

- SHEET 3 BF 4 Johann MICHEL Charlotte LLER lluns- LLER J oqchim IN VENTOR.

A form e y PATENTEDum 26 ten 3,615,719

SHEET 4 [1F 4 Job MICHEL Charlo KELLER Hans-J oachim Y KELLER IN V EN'I'OR.

Attorney APPARATUS FOR INDICATING THE THERMAL HISTORY OF DEEP-FREEZEPRODUCTS PARTICULARLY FOODS The invention relates to a method and toapparatus for indicating the condition, of deep-freeze products, andparticularly foods which are either in a state of deterioration orcompletely spoiled, by means of an indicator provided on the goods or onthe wrapping thereof, in which a signalling medium reacting topredeterminable temperature rises and acts upon a suitable signal bodyto produce a visible alarm.

The increasing use of refrigerated or frozen products, particularlyfoods, necessitates the provision of special testing and control meanswhich are also suitable for bulk goods, both for detecting the state ofrefrigeration of the goods and for checking whether the cold chain fromproducer to consumer has remained intact.

While producers and wholesale distributors have no particulardifficulties in controlling the temperature by means of measuring andcontrol instruments, it may well happen that the goods to be cooled aredamaged by incorrect temperatures during transport or during storage onthe intermediary distributor's or final distributors premises.

It is particularly when a large number of small packages of frozen goodsare to be accommodated in show cases or in open chests on the lastdistributors premises that the purchaser is not always afi'orded theguarantee of receiving perfect goods. Apart from deterioration inquality, there may be injury to health resulting from decomposition ofthe goods by bacteria when the cold chain is interrupted for an extendedperiod of time. In addition, the purchaser is unable readily to detectwhether the food or the luxury food has previously thawed and thenrefrozen and is thus of an inferior quality, is spoiled, or injurious tohealth.

It is known that attempts have been made to reduce these risks byvarious means, for example by means of indicators provided on the goodsto be protected or on the wrapping, so that the respective state ofrefrigeration or the intactness of the cold chain so far may beindicated by deformation or by changes in color.

Thus, for example, chemically or physically reacting indicators areknown which indicate any change in the condition of the goods resultingfrom temperature rises by changing their shape or color or by bursting.Changes of stress occasioned by freezing or thawing in the material ofthe indicators are generally utilized, but the fact that the states ofstress vary in accordance with the rate at which the changes oftemperature take place, is disregarded. The known indicators have theadditional disadvantage that their manufacture, storage, or applicationto the frozen goods is too complicated, or that the readings providedthereby are not sufficiently reliable, or that they cannot bemanufactured at a price in keeping with the value of the goods to beprotected.

It is the object of the invention to avoid these disadvantages and toprovide reliable indicators for the purpose described by simpleinexpensive means. i

Proceeding from the methodhereinbefore described, the invention consistsessentially in that the time interval between the reaction of thesignalling medium and its effect upon the signal body is extended by areaction inhibitor. By this reaction inhibitor, which may be provided,for example, in the form of an intermediate layer, there is noindication given that during harmless temporary temperature rises in thegoods which therefore are not indicated by the indicator. It is onlywhen the total effect of a single temperature rise or of repeatedtemperature rises produces a state of endangering the goods, that thereaction inhibitor is to be overcome by the signalling medium, the alarmbeing then made discernible in the form of changes in color or shape,markings or the like produced by the direct effect upon the signal body.

The invention relates also to numerous constructions of indicators whichare reliable in operation, and can be produced at low cost as describedin the specification and diagrammatically illustrated by way of examplein the accompanying drawing, in which FIG. 1 is a longitudinal sectionthrough a simple indicator according to the invention;

. FIG. 2 is a front elevation of the indicator illustrated in FIG.

FIG. 3 is a cross section through one modification of the indicatoraccording to the invention;

FIGS. 4 to 6 are longitudinal sections through further indicators ofvarious constructions;

FIGS. 7 to 9 are cross sections through indicators provided with lockingmeans;

FIGS 10 and 11 are cross sections of indicators, in which the signalbodies are provided in the form of strips;

FIG. 12 is a plan view of an indicator provided with a spiral signalbody; and

HG. 13 is a cross section through an indicator of a preferredconstruction.

FIGS. 1 and 2 show the principle on which the construction of theindicator according to the invention is based. A casing made of atransparent material 1, is joined by means of an adhesive or by weldingto a counterpiece 2 which may consist of any material. The assembledcasing is subdivided into a signal space 3 which contains a signal body4, and a space or container 5 for a signalling medium 6. In theillustrated construction, the signal body 4 may consist of an absorbentmaterial, such as blotting paper, diatomaceous earth, chalk or the like,whereas the signalling medium 6 consists of a liquid which, uponcombining with the signal body 4 produces a signal, for example bycoloring the signal'area. The space 5 containing the signaling medium issealed off from the signal space 3 by a thin, impermeable partition 8.The signal space 3, provided with the absorbent signal body 4, is closedby an intermediate layer 10 which is dissolved by the signalling medium6. The intermediate layer 10 may consist, for example of molten sugar ofa glassy consistency, egg white, glue, gelatine, albumin, or the like,and when the partition 8 is opened, must first be dissolved by thesignalling medium 6 before the latter can be absorbed by the signal body4 to produce a signal. The interval between the moment at which thesignalling medium 6 is released and the moment at which the signalbecomes visible on the signal body 4 can be predetermined according tothe nature, thickness and composition of the intermediate layer 10.Since the rate at which a given intermediate layer is dissolved isdetermined by the temperature and the time for which the thawedsignalling medium can act upon the intermediate layer, the dissolvingprocess is interrupted whenever a temperature rise has been negligibleor brief, and the signalling medium 6 will refreeze before it reachesthe signal body 4.

Upon the next thawing of the signalling medium 6, the dissolving processof the intermediate layer 10 starts at the position at which it haspreviously been stopped by the freezing process. Thus, the intermediatelayer 10 permits a plurality of negligible temperature rises toaccumulate and thus to be just as effective in producing a reliablesignalling as single or few influences of longer duration which areharmful to the goods.

The container 5 for the signalling medium is opened before or after thefreezing process by the application of a slight pressure to thecontainer 5 for the signalling medium 6, the partition 8 being thuspressed manually or by means of a mechanical device against a suitabledevice, for example a spike 9, and pierced; alternatively as a result ofthe shrinkage of the casing l, 2 due to cold the spike 9 automaticallypierces the partition 8 during the freezing process, or the containerfor the signalling medium is opened, without physical contact, from theoutside by a small piece of metal 25, preferably in the form of a ring,which is provided in the partition 8, and which when the goods, whichmay be in the frozen state, pass through an electric alternating field24, is heated as a result of the formation of eddy currents, and thusopens the partition 8. The alternating field 24 may be operated at anysuitable frequency. When higher frequencies are used, the signallingmedium or portions thereof may serve directly for induction heating. Thepartition may also be opened by mechanical vibrations, particularly ofthe small piece of metal 25, by supersonic control. In exceptionalcases, the focus of a strong source of radiation (light, laser) may beused for opening the partition 8. The space I7 between the partition 8and the intermediate layer 10 serves for indicating by a preliminarysignal that the indicator is ready to indicate when, after the partition8 has been opened, liquid signalling medium (6) (upon opening before thefreezing) or a small quantity of signalling medium which has thawed as aresult of the opening being effected by eddy currents (opening after thefreezing) enters into the space 17.

In order to facilitate the manufacture, the signalling medium may beinserted in a separate container, for example in the form of a capsule,into the indicator casing l, 2, as in a construction illustrated by wayof example in FIG. 3. The projecting edge 30 of the indicator isintroduced into the package of frozen food 32 from the inside andsecured in position by means of an adhesive 31. In this construction,the signalling medium is provided in a cavity 7 of the indicator. Itwill thus be understood that numerous modifications according to heinvention, of which only a few can be shown in the drawings, may bedeveloped.

The signalling medium 6 may consist of a liquid, for example in form ofa self-dyeing staining solution or in the form of a colorless solutionwith dissolved reagents, which produces a color effect only uponcombining with counter-reagents present in the signal space or in thesignal body.

Liquid signalling media 6 of this kind may serve as coloring agentsalone, or a substance (alcohol, glycerol, glycol, sodium chloride,calcium chloride or the like) for fixing the freezing or melting pointat a predetermined temperature may be added thereto.

As illustrated in FIGS. 4 and 5, the signalling medium may also be of apasty, dry or pulverulent consistency, if the signal space 3 or one ofthe compartments of the indicator contains a liquid or a gel and theintermediate layer 10 is adjusted thereto. In this case, the signallingmedium 6 which may consist of a dye powder or of reagents and, with theaddition of a soluble binding agent, may be pressed to producedetermined shapes (balls, pellets, tablets, or hollow bodies). Ifnecessary, the signalling medium may be combined with the solubleintermediate layer. Furthermore, a gas-generating substance, similar toeffervescing with the liquid supplied upon signalling.

An indicator of this construction is illustrated by way of example inFIG. 4. The indicator part turned towards the observer is the signalspace 3 in which the signal becomes visible. The signal space 3 may beprovided with an absorbent layer, for example blotting paper,diatomaceous earth, chalk or the like, or it may contain a liquid asillustrated in FIGS. 4, and 6.

The degree of resistance offered by the intermediate layer to thedissolving power of the thawed signalling medium can be proportioned,for example, by the addition of action of a substance, such as formalin,so that a desired, predeterminable time interval until the intermediatelayer is dissolved by the thawed signalling medium 6 or the equivalentliquid in the signal space 3 is obtained, and a change in color in thesignal space can be detected.

The signalling medium 6 in the indicator is provided in a containerwhich may either form part of the indicator casing (FIGS. l,4,5,6) or aseparate loose container which is inserted into the indicator (FIGS, 3,I0, 11). It is in any case separate from the signal body 4. I

The container for the signalling medium is opened before, during orafter the freezing process manually, or by a mechanical device,orwithout physical contactby the action of electrical or magnetic fieldsby the formation of eddy currents, by supersonic sound, or by the focusof a source of radiation. Opening by the formation of eddy currents hasbeen found to be particularly successful. The opening process mayhowever, also proceed automatically during the freezing process ifsubstances of variable thermal expansion are used, for example asynthetic resin against invar (FIG. 5), or by deformation, using forexample bimetal for the container containing the signalling medium andthe closure thereof (FIG. 6); in this case it is ensured that theopening of the container by the effect of cold is repeated,. The knownutilization of expansion due to freezing for opening the container forthe signalling medium is too unreliable, since so many factors which canbe controlled only with difficulty, play a decisive part, as for examplethe temperature at which the signalling medium is introduced, theresilience of the container for the signalling medium, the degree towhich the container is filled, the freezing velocity according to whichice crystals of completely different shapes and sizes are formed, andwhich may prevent repetition or uniformity of the opening of thecontainer at a given temperature as required for series production, andso on.

Expansion due to freezing when used in addition to the elementsaccording to the invention can at most have the effect of assisting theopening of the container for the signalling medium. In this case, theassisting effect can be improved by providing structural means accordingto hydraulic regularities, so that the relatively high freezing pressurealong short paths is converted into a lower pressure along longer paths.

In utilizing the variable thermal expansion for the opening process, thecontainer for the signalling medium 6 should be made of a material whichis as rigid as possible or which becomes hard and brittle under theaction of cold, or it may be caused by artificial means to shrink or tobecome brittle by thermal or chemical action. The container may,however. also I consist of a separate elastic bag which is inserted intothe indicator if, upon opening (for example by eddy current), thesignalling medium 6 is to be ejected by the wall pressure after thethawing process.

Instead of using the bimetal 15 illustrated in FIG. 6 which is extendedupon freezing and thus pierces the closure 8, an ordinary leaf spring, atoggle joint, or a synthetic resin needle may be used when the parts(15) adapted to pierce are ex tended by magnetic means, for example byan electromagnet 26, through an armature or keeper 27. The closure bywhich the container 5 for the signalling medium is sealed off from thesignal space 3 may consist of a thin layer of material undergoing achange in structure at low temperatures. Thus, for example, a tin foilmay be used which is provided with an addition of grey-tin modification,and which by the effect of cold is transformed completely into the greymodification, increases its volume, and becomes permeable to the liquidsignalling medium 6.

As illustrated in FIG. 7, the signalling medium 6 may also be providedin an open container 5, advantageously provided with a device (a wick, asievelike covering or the like) operating in the manner of a wick. Underthe pressure applied by a spring 12, this container, upon contacting theintermediate layer 10, would cause the intermediate layer to bedissolved by the signalling medium 6 with resultant coloring of thesignal body 4. During the freezing process, the container 5 is releasedby a mechanical device, for example a bimetallic hook l5, and is pressedby the spring 12 against the intermediate layer 10 which cannot,however, be dissolved until it has melted, since the signalling mediumis incapable of reaction when it is in the frozen state.

Instead of the container 5 for the signalling medium being held at adistance from the signal body 4 and from the intermediate layer 10 by amechanical stop, it may also be held in position by a gel 13, forexample silica gel, water glass, or the like, as shown in FIG. 8, inwhich gel the container 5 for the signalling medium is anchored atnormal temperatures and during the period of freezing. The gels referredto have the property of undergoing a structural conversion by thefreezing process and thus after having rethawed cease to have theproperties of gels and assume the properties of the liquids. For thisreason, the anchorage of the container 5 for the signalling medium,which anchorage is reinforced by ribs of fins I4, is released after thegel has thawed, and the container then contacts the signal body 4 or theintermediate layer 10 forwardly thereof, the layer being dissolved whenthe signalling medium 6 has thawed.

The intermediate layer 10 is dissolved by the signalling medium 6irrespective of the particular releasing process by which it is broughtinto contact with the layer, so that the resultant signal becomesvisible on the signal body 4 in the signal space 3. This signal mayoriginate from the coloring signalling medium 6 being simply absorbed byan absorbent layer, or it may originate from a chemical reactioninvolving change of color when the signal body 4 or an equivalent liquidand the signalling medium 6 are impregnated with suitable reagents. Analarm reaction may also be obtained when the colored signal body 4 orparts thereof (for example characters or symbols) are bleached by thesignalling medium 6, in that the signal body 4 assumes a different colorafter the signalling.

The signal body permits of mainfold variations of signalling. Wheninvisible symbols, characters or the like are printed on the signalbody, for example white on white, such symbols will become visible assoon as the signal body 4 is caused by the signalling medium 6 to assumea different color at the unprinted positions. Similarly, visible symbolsprovided on the signal body 4 may disappear when such symbols are, forexample red and the signal body assumes the same tone of color.

- Appearing and disappearing characters or symbols may be combined withpermanently legible characters or symbols, for example black charactersor symbols, as desired.

The nature of the signalling medium may be such that, when it penetratesinto the signal layer by combining with a particular substance, there isreleased for example sodium carbonate, an acid, or a gas, such as carbondioxide, by which part of the indicator casing l is inflated, so thatthe reading in the indicator is in addition perceptible with the aid ofsmall, for example wartlike, projections which can be felt by touch byblind, ambylopic or color blind persons. As illustrated in FIGS. 1, 4, 5and 6, the indicator may, if necessary be so constructed that thedischarge of the signalling medium 6 from the container 5 for thesignalling medium and the contact with the intermediate layer in generalare made visible by a preliminary signal. In one construction similar tothose illustrated in FIGS. 3, l and ll, this preliminary signal can beproduced by limiting a small section of the signal body 4 by means of animpregnation, no retarding intermediate layer being provided at thatposition, so that, when the container for the signalling medium has beenopened, a punctiform marking is produced by a minute portion of thesignalling medium. While the preliminary signal may be of no particularimportance to the consumer, it is extremely important to the frozen-foodproducer, since he is thereby enabled to detect the readiness of theindicator to produce a signal.

FIG. 9 shows by way of example one type of indicator, in whichcharacters, symbols or the like of iron powder 19, for example carbonyliron, are formed by the action of a magnetic or electric device 26 onthe signal body 4, advantageously forwardly or at the back internally ofthe indicator casing, and fixed in the arranged order by application ofthe intermediate layer 10. The liquid in form of a gel I3 is thenintroduced into the intermediate layer [0 until it has thawed, andchanged its structure after the freezing process, as hereinbeforedescribed, and assumes the properties of a liquid.

When the intermediate layer 10 has been dissolved by a liquefied gel 13,the characters or symbols formed by mag netic action will disintegrate.Instead of applying an iron powder to produce the characters andsymbols, such characters or symbols may consist of a material, forexample a dye, which is soluble in water, so that they fade or aredissolved after the dissolution of the intermediate layer 10.

It may be desirable or necessary for the length of time for which thecold chain has been interrupted as well as for the occurrence ofatemperature rise in the goods to be protected, to be detected. For thisreason, the signal body 4 provided in the construction illustrated inFIGS. 10 to 12 is so constructed as to enable it to record the timeinstead of or in addition to producing the usual reading. Indicators ofthis kind are based in the principle that in the operative state theindicator not only indicates by means of a color signal on the signalbody 4 that a prescribed temperature has not been,maintairied but itindicates simultaneously that signalling medium 6 is absorbed along anadditional, longer signal path 20. A signal path of a determined lengthmay be obtained, for example by providing it in the form of a spiralenclosing the signal body 4 proper. It may, however, also be of arectilinear, undulating or zigzag shape; that is to say, it may have anydesired shape. The rate at which the signalling medium is absorbeddepends upon the absorption properties of the signal paths 20, so thatthe length of time for which the indicator has operated results from thecoloring distance covered.

The absorptivity of the signal paths 20 may be slowed down oraccelerated by impregnation with a colloidal or strongly hygroscopicsubstance, so that the period of time for which the reading is requiredto last can be selected within wide limits.

The signal paths 20 are provided with a graduated scale 21 on which thetime interval during which the temperature has deviated from a giventemperature is indicated. A plurality of signal paths 20 which may, ifdesired, have various absorption velocities and, if necessary, mayproduce various colors, may be used simultaneously. Different colors maybe produced by one and the same signalling medium 6 provided thesignalling medium contains for example an iron salt, whereas the signalpaths 20 are impregnated with a thiocyanate and potassium ferrocyanide,so that the recording of the time proceeds progressively on one path inred and on the other path in blue.

The manufacture may be simplified by using as the signal body 4, forexample a disc or the like which is absorbent throughout and which ischanged by the application of a substance 22 by which its absorptivecapacity is eliminated (for example by being printed with an oil color,a wax color, or the like) with resultant determination of the shape,width, length and course of the signal paths which retain theirabsorptive capacity. It will be understood that the signal paths 20 mayalso be stamped and filled with the absorbent material as illustrated inFIG. 11.

The absorbent body may, for example, also be provided in the form of adevice used for producing screen-printing stencils simply by filling thestencil with the absorbent material at the positions which remainpermeable, unless the supporting fabric of the stencil is itselfsufficient to act as an absorbent material by capillary action (in themanner ofa wick).

A thin transparent or translucent flexible tube made, for example, ofasynthetic resin, may be used which, having a suitable shape, for examplethe shape of a spiral, represents the signal paths 20 as a result of thecapillary action. In addition, the capillary tube may be wetted orcoated with a hygroscopic substance on the inside.

in order to avoid extraneous influences (drying up, moistening, or thelike), the indicator is enclosed by a casing which is wholly orpartially transparent or translucent and advantageously made airtight bymeans of an adhesive or by welding.

One preferred construction according to the invention, in which allaspects are taken into account, is diagrammatically illustrated by wayof example in FIG. 13. The section 2 of the casing assembled from twosections 1 and 2 is provided with a cavity 7 which contains athin-walled, elastic, baglike container 5. The container Sis filled withthe signalling medium 6 consisting of an aqueous color solutioncontaining an addition of glysantine. The filled bag 5 is pressed intothe cavity 7 by an insert ll stamped out from a synthetic resin foil.The insert 11 contains a stamped-out disc of blotting paper 4 providedwith a hole in the center and coated on its underside with a solublelayer 10 of glue slightly fermented with formalin.

The stamped cavity provided centrally of the insert 11 contains a window16 for the preliminary signal, the window 16 containing also a smalldisc of blotting paper 4, however, without the soluble layer 10.Provided below the small disc 4 is a small ring 25 of thin wire which isheated for a very short period of time before, during or after thefreezing process by being moved without physical contact past a coil 24of an electric alternating field.

The transparent section 1 of the casing is provided above the insert 1 1and is welded or glued at its edge to the section 2 of the casing. Theedge, which may be provided, for example, with a self-adhesive coating,serves also for securing the indicator lightly to a package of frozenfood on the inside.

The indicator may be produced at normal ambient temperature, stored asdesired, and provided on the goods to be frozen. Before, during, andparticularly after the freezing process, the goods are released by beingmoved on a conveyor belt past the coil of an electric alternating fieldof a suitable frequency, in which a locally limited section of the smallmetal wire 25 is heated by the formation of eddy currents, and the bagis thus opened.

The small amount of signalling medium 6 temporarily melted by theopening process while the remainder remains frozen can now act upon thesmall area 4' of the signal body 4. This area is thus colored toindicate in the signal window that the indicator is released and thusready to indicate impending temperature rises.

When the temperature rises above the melting point of the signallingmedium 6, which melting point is predetermined by the addition ofgylsantine, the signalling medium becomes fluid and, under the wallpressure of the bag 5 and as a result of the capillary action, passesthrough the openings 18 to the intennediate layer thus starting todissolve it.

When a temperature rise is only a brief and negligible one and the goodsstill remain undamaged, the dissolution of the intermediate layer 10 isinterrupted upon refreezing of the signalling medium. At the nexttemperature rise, the dissolving process will start at the same positionat which it has previously been interrupted until the sum of severaltemperature rises which individually have been harmless, produces asignal in exactly the same manner as a single temperature rise of longduration when the intermediate layer 10 is dissolved and the signallingmedium 6 is capable of penetrating into and coloring the signal area 4.Signals of any color may be produced.

The coloring of the signal area is irreversible. As hereinbeforedescribed, the signal area may be provided with characters or symbols ofany combination which may appear or disappear at each signalling orwhich may be permanently visible. By using a signal area of a differentkind, the indicator may also serve for signalling with time-recordingwithout any alteration being required, so that it indicates not only theinterruption of a cold chain, but in addition for how long the coldchain was interrupted from the moment at which the indicator started tooperate.

Owing to the fact that the cavity 7 with the signalling medium 6 extendsinto the package of frozen food, it isin close contact with the frozengoods and thus highly insensitive to false alarm caused by extraneousinfluences.

We claim:

1. A system for indicating the thermal history of packaged deep-frozengoods comprising:

a first sheet formed with a transversely extending cavity;

a second sheet bonded to said first sheet over said cavity andtransparent at least over said cavity to provide a signal window, saidsecond sheet being provided in a wall of a frozen-goods package;

a body of signalling liquid in said cavity having a melting temperatureabove the deep-freeze temperature of said goods but below 0C.

a liquid impermeable partition containing said body of liquid;

a fiat reaction-inhibiting layer overlying said cavity between saidsheets and lying in a plane transverse to the cavity but parallel tosaid sheets, said layer being composed of a material soluble in saidliquid for retarding passage of same;

a flat signalling layer overlying said reaction-inhibiting layer betweensaid sheets and being of a material capable of reacting with said liquidto produce a signal visible through the window of said second sheet anda spike avlng a pointed end adjacent and directed transversely to saidfirst sheet toward said partition and capable of piercing said partitionto permit the flow of melted signal liquid therethrough the other end ofsaid spike, bearing on one of said layers, whereby piercing of saidpartition by said spike activates said system.

2. A system for indicating the thermal history of deepfrozen goodscomprising:

a receptacle attached to said goods;

a component in said receptacle having a melting temperature above thedeep-freeze temperature of said goods;

an adsorbent component in said receptacle capable of reacting with thefirst-mentioned component to produce a visible indication;

an impermeable meltable partition separating said components in saidreceptacle;

a spiked metallic body in engagement with said partition;

and

means adjacent the metallic body for generating an alternating-currentelectric field and therewith including eddy currents in said body toheat same and thereby melt and opening in said partition wherebyformation of said opening activates said system.

3. The system defined in claim 2, further comprising:

a reaction-inhibiting layer adjacent said partition and composed of amaterial soluble in said first component for re tarding passage of same.

4. A system for indicating the thermal history of deepfrozen goodscomprising:

a receptacle attached to said goods;

a component in said receptacle having a melting temperature above thedeep-freeze temperature of said goods;

an adsorbent component in said receptacle capable of reacting with theother component to produce a visible indication;

an impermeable meltable partition separating said com- I ponents in saidreceptacle;

a reaction-inhibiting layer between said partition and said adsorbentcomponent and composed of a material soluble in said other component inthe liquid form thereof for retarding passage of the same;

a spiked metallic body in engagement with said partition,

said layer being interrupted adjacent said body; and

means adjacent the metallic body for generating an alternating-currentelectric field and therewith inducing eddy currents in said body to heatsame and thereby melt an opening into said partition, whereby formationof said opening activates said system and create visible indication onlyadjacent said body.

5. A system for indicating the thermal history of deepfrozen goodscomprising:

a receptacle attached to said goods;

a liquid component in said receptacle having a melting temperature abovethe deep-freeze temperature of said goods but below 0C.

an adsorbent component in said receptacle capable of reacting with saidliquid component to produce a visible indication;

an impermeable metal partition separating said components in saidreceptacle;

a reaction'inhibiting layer between said partition and said adsorbentcomponent and composed of a material soluble in said liquid component inthe liquid form thereof for retarding passage of same and reaction ofsame with said adsorbent component, said layer being interruptedadjacent a limited portion of said adsorbent component; and

a spiked metal body juxtapositioned with said partition and adapted topierce the same upon movement there against for activating said systemand creating a visible indication only at said portion.

l I! t I! ll

2. A system for indicating the thermal history of deep-frozen goodscomprising: a receptacle attached to said goods; a component in saidreceptacle having a melting temperature above the deep-freezetemperature of said goods; an adsOrbent component in said receptaclecapable of reacting with the first-mentioned component to produce avisible indication; an impermeable meltable partition separating saidcomponents in said receptacle; a spiked metallic body in engagement withsaid partition; and means adjacent the metallic body for generating analternating-current electric field and therewith inducing eddy currentsin said body to heat same and thereby melt and opening in said partitionwhereby formation of said opening activates said system.
 3. The systemdefined in claim 2, further comprising: a reaction-inhibiting layeradjacent said partition and composed of a material soluble in said firstcomponent for retarding passage of same.
 4. A system for indicating thethermal history of deep-frozen goods comprising: a receptacle attachedto said goods; a component in said receptacle having a meltingtemperature above the deep-freeze temperature of said goods; anadsorbent component in said receptacle capable of reacting with theother component to produce a visible indication; an impermeable meltablepartition separating said components in said receptacle; areaction-inhibiting layer between said partition and said adsorbentcomponent and composed of a material soluble in said other component inthe liquid form thereof for retarding passage of the same; a spikedmetallic body in engagement with said partition, said layer beinginterrupted adjacent said body; and means adjacent the metallic body forgenerating an alternating-current electric field and therewith inducingeddy currents in said body to heat same and thereby melt an opening intosaid partition, whereby formation of said opening activates said systemand create visible indication only adjacent said body.
 5. A system forindicating the thermal history of deep-frozen goods comprising: areceptacle attached to said goods; a liquid component in said receptaclehaving a melting temperature above the deep-freeze temperature of saidgoods but below 0*C. an adsorbent component in said receptacle capableof reacting with said liquid component to produce a visible indication;an impermeable metal partition separating said components in saidreceptacle; a reaction-inhibiting layer between said partition and saidadsorbent component and composed of a material soluble in said liquidcomponent in the liquid form thereof for retarding passage of same andreaction of same with said adsorbent component, said layer beinginterrupted adjacent a limited portion of said adsorbent component; anda spiked metal body juxtapositioned with said partition and adapted topierce the same upon movement there against for activating said systemand creating a visible indication only at said portion.